The bithorax complex in Drosophila melanogaster contains a number of closely linked genes, mutants of which profoundly influence the determination and subsequent development of those larval imaginal discs forming the thorax and anterior abdominal segments of the adult fly. Genetic studies of this gene complex have suggested that the complex may represent a type of operon whose function is to control the developmental potential of the imaginal discs. The purpose of the proposed research is to elucidate the biochemical basis for the observed mutant function in controlling the developmental pathway followed by a given imaginal disc during differentiation. RNA-DNA hybridization techniques will be developed to detect messenger RNA transcribed from the complex. Studies will then be undertaken with mutants to determine if a polycistronic messenger is transcribed from the complex as is suggested by genetic studies. DNA binding studies, among others, will be employed to attempt to detect proteins which may be coded by some of the genes in the bithorax complex, making use of mutants which appear not to make gene products as well as other mutants which appear genetically to be over-producers of gene products. Related studies on the structure of the DNA in both interphase and metaphase chromosomes as well as in polytene chromosomes of D. melanogaster will be undertaken. Efforts will be made to determine if a subunit structure exists in the DNA of chromosomes and if such subunits might lend themselves to a biologically meaningful fractionation of the genome into specific genetic regions, e.g. the bithorax region.